The invention relates to a method of producing a plate of steel, in particular one having a thickness of more than 50 mm, by hot-rolling a prematerial in several passes.
In steel construction engineering, in particular for the construction of nuclear power plants, plates of large thicknesses, such as, e.g., of up to 300 mm and more, are required to an increasing extent. The production of such thick plates hitherto has involved great difficulties. It is known for the production of plates, to start from cast ingots of suitable sizes. In order to achieve perfect qualities of the ready plates, a minimum degree of deformation has to be observed when processing them; this minimum degree of deformation is determined in accordance with the quality demands. As a rule, it is more than five; the ingot size depends on the minimum degree of deformation; therefore, with thick plates, ingot weights of between 15 and 60 t are reached.
Ingots of this size cast in a conventional manner are known to be very inhomogenous; the foot section tends to being enriched by inclusions, the head section is segregated and full of pipes reaching as far as to the middle of the ingot. These properties of large ingots, as a result, often cause impermissible failures to be detected in the ready plate by ultrasonic testing, calling for a devaluation or even scrapping of the plates. Also are the mechanical-technological properties of these plates from large ingots, in particular the mechanical-technological properties in the thickness direction, insufficient.
In order to avoid these difficulties, it is known to produce ingots according to special methods, which are, however, very complex and also very expensive due to the high energy consumption involved. Such special methods are the electroslag remelting method (ESR-method) or the Bohler electroslag topping method (B.E.S.T. method).